Kyle Flack, 20, suffocated to death at Basildon hospital in 2006 when his head became wedged in the bars of his bed. Photograph: PA

The NHS is accused of causing or contributing to the deaths of at least 74 patients with a learning disability because of poor care that reveals enduring "institutional discrimination" among doctors and nurses.

The 74 vulnerable patients' deaths over the past decade were either caused or complicated by mistakes in hospitals and decisions by staff who failed to treat them properly and displayed ignorance or indifference to their plight, according to the charity Mencap and families of some of those who died.

Inquiries by Mencap into the deaths raise searching questions for the NHS, which has been criticised in a series of recent reports for providing poor care, especially to older patients. The parliamentary and health service ombudsman, Ann Abraham, has already ruled that four of the cases highlighted were avoidable deaths and found serious failings in eight others. Inquest verdicts also confirm failings occurred in several cases.

"These cases are a damning indictment of NHS care for people with a learning disability," said David Congdon, Mencap's head of campaigns and policy. "They confirm that too many parts of the health service still do not understand how to treat people with a learning disability and they are an appalling catalogue of neglect and indignity. As a result of institutional discrimination in the NHS, people with a learning disability are dying when their lives could be saved."

While the NHS had taken a lot of positive steps since the charity's Death by Indifference report in 2007, "we are still hearing of many patients with a learning disability receiving poor treatment", he said. "Sadly, we believe that the cases in this report represent the tip of the iceberg," he added.

The 74 cases show that advice from the families of people with a learning disability has gone ignored, staff have failed to diagnose serious illness in them, patients have been denied basic nursing care and been left in excruciating pain after being denied medication, while some staff have assumed that some learning disabled patients' quality of life is so low that they are not worth saving, according to Mencap.

Ministers endorsed the charity's concerns on Monday and promised changes to improve staff's care of these patients. Paul Burstow, the care services minister at the Department of Health (DH), said: "This government is committed to improving the health of people with learning disabilities. We share Mencap's concerns that some people with learning disabilities are not receiving the high quality health care that they should expect."

Existing concern about treatment of such patients has prompted the DH to act. "We have extended the contract for a government-funded confidential inquiry into the premature and avoidable death of people with learning disabilities. We are also funding a specific public health observatory focusing on improving healthcare for people with learning disabilities," said Burstow.

He added: "Those providing care – whether NHS, charity or private sector – have a duty to make sure that care is high quality and safe."

NHS bosses pledged to look closely at Mencap's dossier. "One of the measures of a civilised society is how well it looks after the most vulnerable members of its society," said Professor Sir Bruce Keogh, the NHS's medical director. "So I take very seriously any evidence that this is not reflected in our NHS. I look forward to seeing the Mencap report."

Mencap's evidence highlights cases such as:

• Carole Foster, whose care at Fairfield hospital in Bury before she died in 2006 aged 52, was so bad that her death was avoidable, said the ombudsman after investigating.

• Lisa Sharpe, who died aged 21 in 2004 and is one of four deaths among the 74 to have occurred at Basildon hospital in Essex. The hospital was guilty of "service failure", the ombudsman ruled.

• Nine-year-old Daisy Healy, whose NHS care before she died in 2005 led the ombudsman to criticise "service failure" which meant that both she and her family "suffered injustice".

• Kirsty Pearce, whose death in 2003 – again after being looked after at Basildon hospital – prompted the ombudsman to reach findings of "significant failings" in her care.

The confidential inquiry is investigating deaths of all patients with learning disabilities in five primary care trust areas in south-west England, whether controversial or not, to see whether anything more could be done to prevent them dying in NHS care. It will make recommendations to ministers in 2013.

"People with learning disabilities have the right to receive timely, appropriate and individually-tailored care to meet their needs in the same way as anyone else has. It is outrageous for these rights to be doubted or neglected," said Dr Pauline Heslop, the inquiry leader.

Professor Steve Field, chair of the NHS Future Forum, which advises the government on health policy, backed Mencap's demand for NHS staff to undergo fuller training to help them better understand such patients and improve their communication with them.

"During our listening exercise we heard from patients and staff that health professionals working in the NHS need better training in dealing with such complex and challenging patients," Field said.

"At our meeting with young people at Birmingham City hospital we heard from them that doctors and nurses need better understanding of the needs of people with learning disabilities and mental illness — and that this should be an important part of their training."